To check the thermostat on a car, start a cold engine and touch the lower (outlet) radiator hose with your hand - it should be cold. After the coolant temperature reaches 90-95°C, the hose should begin to heat up quickly, which indicates that the liquid has begun to circulate through the large circuit of the cooling system. If this does not happen, remove the thermostat and replace it.
You will need a 10 mm wrench.
1. Drain the coolant (see "Replacing the coolant").
2. Remove the three thermostat cover mounting bolts...
3. ... remove the lid...
4. ...and remove the thermostat from the cover.
5. Remove the sealing ring from the thermostat and inspect it. Replace any ring that is too compressed, hardened or torn.
6. Install the O-ring onto the new thermostat.
7. Install the parts in the reverse order of removal.
8. Fill the coolant and remove air locks from the cooling system (see "Replacing the coolant").